Now new Gmail for iOS allows you to add support for signing out of a single account.

 Google continues global integration within its services and applications. This means, Google services are more and more interconnected. Henceforth, we the release of the version 2.2.7182, if installed YouTube, Google Maps and Chrome links now go
directly to the app instead of the mobile web.
It can also include Added support for signing out of a single account.

For those who unfamiliar, with the Gmail app, you can: Search through all your mail quickly with predictions as you type ;  See profile pictures as part of the conversation ; Read your mail with threaded conversations ;  Read and respond to interactive Google+ posts right from the app ;  Send and receive attachments ; Customize emails with custom scribbles and so on.